Mattress cover



FIG. 1 is a bottom perspective view of an ornamental design for a mattress cover;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a back elevational view thereof; and,

FIG. 4 is an expanded detailed view of the encircled area 4 of FIG. 3 showing an opening for receiving a valve of an inflatable mattress which is shown in broken lines.

Dashed features illustrate environmental structure and form no part of the claimed design. 

CLAIM The ornamental design for a mattress cover, as shown and described. 